This disclosure relates generally to the field of wireless network communication, and in particular to a method and apparatus configured to provide a 802.11 very high throughput (VHT) preamble signaling field with legacy compatibility.
Wireless communication systems may operate in accordance with one or more protocol standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems(LMDS), multi-channel-multi-point distribution systems (MMDS), and the like. The applicable protocol for wireless communications standard may vary. As the IEEE 802.11 specification has evolved from IEEE 802.11 to IEEE 802.11b (standard 11b) to IEEE802.11a (standard 11a) and to IEEE 802.11g (standard 11g), wireless communication devices that are compliant with standard 11b may exist in the same wireless local area network (WLAN) as standard 11g compliant wireless communication devices.
When legacy devices such as those compliant with an earlier version of a standard reside in the same WLAN as devices compliant with later versions of the standard, mechanisms or processes may be employed for the legacy devices to know when the newer version devices are utilizing the wireless channel to avoid interference or a collision. A legacy system may be an existing system that is in place and available for use in wireless local area networks. The issue of legacy systems may be important because these systems may remain in place after new standards, methods or networks for future wire local area networks are implemented.
The different protocols or standards may operate within different frequency ranges, such as 5 to 6 gigahertz (GHz) or, alternatively, 2.4 GHz. For example, standard 11a may operate within the higher frequency range. An aspect of standard 11a is that portions of the spectrum, between 5 to 6 GHz, are allocated to a channel for wireless communications. The channel may be 20 megahertz (MHz) wide within the frequency band. Standard 11a also may use orthogonal frequency division multiplexing (OFDM). OFDM may be implemented over subcarriers that represent lines, or values, within the frequency domain of the 20 MHz channels. A signal may be transmitted over different subcarriers within the channel. The subcarriers may be orthogonal to each other so that information or data is extracted off each subcarrier about the signal.
Backward compatibility with legacy devices may be enabled at the physical (PHY) layer. At the PHY layer, backward compatibility is achieved by re-using the PHY preamble from a previous standard. Legacy devices may decode the preamble portion of all signals, which provides sufficient information for determining that the wireless channel is in use for a specific period of time, to avoid interference and collisions even though the legacy devices cannot fully demodulate or decode the transmitted frame(s).
As new standards or protocols are implemented, backward compatibility of receiving and transmitting signals may become more of a concern. New signaling formats may desire more robustness than legacy formats. Further, frames exchanged within a wireless system may include immediate acknowledgement capabilities, bursting information and exchanging more bits of information than frames used by legacy devices. It is desired to provide a very high throughput preamble signaling field that is compatible with legacy STAs.